1. Technical Field
The present invention relates to fiber optic cable and, more particularly, to a method and apparatus for protecting the optical fibers of a fiber optic transmission cable.
2. Background Art
Over the years, fiber optic cables have gained popularity and are used in a variety of fields. One such field is oil and gas exploration where fiber optic systems are used for measuring certain conditions underground, such as temperature, pressure, acceleration and vibration. Fiber optic cables extend from surface instrumentation through a wellhead and connect to measurement devices disposed in an underground region to transmit data indicating status of the underground condition to the surface.
A gas and/or oil exploration environment is harsh, characterized by well fluids, extreme temperatures and pressures, and multiple other cables and equipment extending downward through the well into the underground region. The optical fiber is typically fragile and must be shielded from the harsh well environment. To effectively protect the optical fiber from the well environment, the fiber is placed into protective metal tubing and is environmentally sealed therein.
However, a problem arises when sections of the protective tube, or outer capillary tube, must be terminated or connected either during assembly, installation and/or repair. During assembly and installation, segments of the tubing must be joined and sealed to form a continuous protective covering for the long optical fiber. Similarly, when the fiber optic cable must be terminated and repaired or spliced, the metal protective tubing is cut to gain access to the optical fiber, after which the fiber optic cables must be spliced and the cut ends of the protective tubing must be joined or effectively terminated.
After an optical fiber has been cut, the characteristics of the xe2x80x9cfiber friendlyxe2x80x9d termination of the optical fiber as it exits the metal tube is critical, namely for enhanced mechanical reliability offered via the strain relief transition between the rigid metal tube and the fragile fiber. For severe environmental conditions, such as high temperature and vibration applications, the termination must provide isolation of strains exerted on the fiber as a result of differential expansion between the metal tube and fiber, sealing to prevent migration of the fluid and blocking grease from flooding other components and an anti-chaffing feature to protect the fiber where it exits the metal tube. Traditionally, termination of the optical fiber is provided via the bonding or molding of a rubber boot at the fiber exit point from the metal tube. Bonding or molding operations tend to be either too complex or too time consuming for use in the field. Moreover, applications requiring fixturing of the fiber for isolation of modest strains 0.2% (e.g. high temperature installations) necessitate bonding directly to the fiber and which may require stripping of the buffer coating protecting the fiber. This presents the potential for damaging the delicate glass fiber that could precipitate an immediate failure or fail at some point after the system installation, making quality control problematic. What is needed is an optical fiber termination technique which does not require removal of the buffer material and which provides strain relief, and which positively locks and seals the fibers at their terminus from the metal tube.
The joint between the ends of the outer capillary tube must be environmentally sealed to prevent well contaminants from contacting the optical fiber. One known method of environmentally protecting the optical fiber is to use a tray or cabinet to house the fibers. It is not always possible to utilize trays or cabinets to protect the optical fibers because of space constraints. Welding of the metal outer capillary tube is another, and most practical, method for joining the ends of the outer capillary tube during either an assembly, installation and/or repair, because it is the best guarantee for environmental seal. However, the heat and UV light generated by welding can potentially result in damage to the optical fiber disposed inside the outer capillary tube. One method for protecting the optical fiber during a welding operation is disclosed in European Patent Application Number EP0689799A2 that shows the insertion of a metal tube adjacent to the optical fibers. This method would protect the fibers from the UV light but would conceivable conduct a great deal of heat to the optical fibers.
Therefore, there is a need for a method and apparatus for facilitating attachment of the outer capillary tube ends during assembly, installation or repair.
It is an object of the present invention to provide a method and apparatus to protect optical fibers within a transmission cable and to further facilitate joining ends of a pair of fiber optic transmission cables during assembly, installation or repair.
According to the present invention a heat sink for use during assembly, installation and/or repair of a fiber optic transmission cable includes a heat sink tube disposed within an outer capillary tube of the transmission cable with the optical fiber enclosed within an inner capillary tube and passing through the heat sink tube. The heat sink tube is crimped to the outer capillary tube and is comprised of a material having a high heat conductivity. During the assembly of a splice protector in accordance with the present invention a splice tube is welded to the outer capillary tubes and the heat sink tubes dissipate the heat from the welding process thus protecting the optical fibers from heat damage.
It is another object of the present invention to provide strain relief for optical fibers of a fiber optic transmission cable near the cable termination. In accordance with the present invention a fiber strain relief mechanism for use during assembly, installation and/or repair of a fiber optic transmission cable having an outer capillary tube enclosing at least one optical fiber having a coating material, includes a compliant tube captured within a carrier tube attached to the outer capillary tube. The carrier tube is crimped with the outer capillary tube capturing the coated optical fiber within the compliant tube. In a particular embodiment the compliant tube is comprised of an elastomeric material.
It is further an object of the present invention to provide a splice protection assembly for use in joining the ends of a pair of fiber optic transmission cables where the fiber optic transmission cables include an inner capillary tube enclosing at least one coated optical fiber positioned within an outer capillary tube. In accordance with the present invention the splice protection assembly includes a heat sink tube crimped within the outer capillary tube the end of each cable. An optical strain relief mechanism is crimped within each heat sink to capture the coated optical fiber therein to provide strain relief for a splice that joins the fiber pairs together. A sealing assembly is further included and is positioned on the inner capillary tube within the outer capillary tube and provides a seal therebetween. In a particular embodiment the sealing assembly includes an o-ring positioned between a seal washer and an end plug which cooperate with the heat sink to bias the o-ring against the outer capillary tube. A splice tube is positioned over the fiber splice and is welded to the outer capillary tubes. In alternative embodiments of the present invention a pair of weld couplings is included and is positioned at the ends of the splice tube and both are welded to the splice tube and to the fiber optic transmission cables. The present invention further includes a non-rigid splice sleeve installed over both of the heat sinks covering the optical fiber splice area. The sleeve protects the fiber splice from damage during installation of the splice tube. The heat sink tubes protect the optical fibers during the welding of the splice tube and weld couplings.
It is yet a further object of the present invention to provide a method of protecting a splice between the ends of a pair of fiber optic transmission cables where the fiber optic transmission cables includes an inner capillary tube enclosing at least one coated optical fiber positioned within an outer capillary tube. In accordance with the present invention the method includes the crimping of a heat sink tube within the outer capillary tubes while feeding the optical fiber through the heat sink tube and through a fiber strain relief tube. Crimping the fiber strain relief tube within the heat sink tube captures the optical fibers. The method further includes the installation of a splice tube by sliding the splice tube over one of the fiber optic transmission cables. A fiber optic splice is performed and the splice tube is positioned over the optic fiber splice. Welding the splice tube to the fiber optic transmission cables protects the splice area. Sealing of the splice area is accomplished in accordance with present invention by installing a sealing mechanism on the inner capillary tube within the outer capillary tube. In particular embodiments of the present invention the venting gases heated during welding step is accomplished by venting them through a vent hole positioned in the outer capillary tube, however, internal to the splice tube.
One advantage of the present invention is that it simplifies the installation and repair procedures in the field and assembly process during manufacturing. Another advantage of the present invention is that it provides strain relief to the coated fibers within the fiber splice area. Yet another advantage of the present invention is that it provides seal protection to the splice area.
The foregoing and other advantages of the present invention become more apparent in light of the following detailed description of the exemplary embodiments thereof, as illustrated in the accompanying drawings.